A conveying wheel of a half-shell-like design is equipped with a plurality of blades following each other in the circumferential direction around an axis of rotation of a conveying wheel, for example, in so-called side channel fans, as they are used in parking heaters or auxiliary heaters of motor vehicles to convey the combustion air. This conveying wheel rotates with its area carrying the blades above a ring channel at a housing, which ring channel is open on its side facing the conveying wheel. Due to the rotation of the conveying wheel, the air to be conveyed is drawn in through an inlet opening, compressed and conveyed forward and released in the area of an outlet opening. A so-called interruption, by which the channel provided in the housing, which otherwise passes through in an annular pattern, is interrupted, is arranged between the inlet opening and the outlet opening.
Periodic excitations are generated due to the fact that blades move periodically past stationary component areas, e.g., the interrupter, during the conveying operation. The excitation frequency corresponds to the speed of the conveying wheel multiplied by the number of blades provided at the conveying wheel. A so-called edge tone with a characteristic frequency in the range of about 1,500 Hz, which is superimposed to the rest of the noise spectrum and markedly differs from this spectrum, may be generated by this excitation. To reduce the perceptibility of this tone or such noises, mufflers are frequently used to make it difficult to transport the noise in the medium being conveyed, i.e., the air.
A side channel fan, in which the blades are arranged at irregular relative distances from one another to avoid such characteristic noises, is known from DE 39 39 957 A1. The deviation of the mutual distance is suggested here to be in the range of ±20%, and the distribution is the to be, in principle, statistical, and it is the that all the distances may even be different from one another, even though the development of an imbalance shall be prevented from occurring by corresponding positioning of the blades.